Analogy!

Definition: a comparison of two or more similar objects, suggesting that if they are alike in certain respects, they will probably be alike in other ways as well.

Example:

A street light is like a star. Both provide light at night, both are in predictable locations, both are overhead, and both serve no function in the daytime.

Link:
http://www.youtube.com/watch?v=QuldqadgUxE